Electrophotographic coating containing finely divided photoconductor in a synthetic polymer having ionizable functional groups



United States Patent US. Cl. 96-]..8 19 Claims ABSTRACT OF THE DISCLOSURE A process is described wherein a pattern of electrostatic charges is formed on the surface of electrophotographic image carrier comprising a base and an electrically insulating coating including a photoconductor in a synthetic organic polymer. The polymer contains functional groups ionizable in an aqueous solution containing an electrolyte. The pattern of electrostatic charges is developed with electrostatically attractable material.

This application is a continuation of application Ser. No. 640,353, filed Feb. 15, 1957, now abandoned, and assigned to the same assignee as this application.

This invention relates to electrophotographic reproduction processes and, more particularly, to an electrophotographic or electrophotosensitive coating material therefor including Water soluble binders and dispersed solids adapted to be applied from water solution.

Electrophotographic or electrostatic reproduction processes of the character to which this invention relates include processes such as are disclosed in the copending application of Greig, Ser. No. 383,677, filed Oct. 1, 1953, and assigned to Radio Corporation of America, now Patent 2,898,191 issued Aug. 4, 1959, and comprises generally the steps of impressing an electrostatic charge on a plate or paper or other image carrier base or sheet having an electrophotographic or electrophotosensitive surface, exposing the charged surface to a light image whereby portions of the charged surface corresponding to the light image are discharged to form an electrostatic image or pattern, and rendering the electrostatic pattern visible or developed by applying thereto a visible developing agent or powder having electrostatic charge characteristics such that it will be attracted to the charged areas and not to the discharged areas of the exposed surface, or vice versa.

Generally, as will be understood, the electrostatic or electrophotosensitive surface of such a plate or sheet or other image carrier base material may comprise a coating of an electrophotosensitive material in a film forming binder forming a matrix-type of surface on which an image may be electrophotographically reproduced. 'In such a matrix surface, the film forming binder for the electrophotosensitive or photoconductor material should have appropriate dielectric and/or electrical characteristics such that the surface may be given an appropriate electrostatic charge prior to being exposed to the light image.

Accordingly, it has previously been believed that the dielectric or electrical characteristics required that the film forming binder be water insoluble in order, among ice other reasons, to avoid possible electroconducting effects usually associated with an electrolyte or ionisable water soluble material.

In using water insoluble film formers to produce such an electrophotosensitive surface, however, difiiculty may be experienced in coating the sheet or image carrier base with an organic solvent solution because of the required presence of organic solvents therein. Other difficulties may be experienced in keeping the photoconductor or photosensitive material, which is usually if not always an inorganic material, adequately dispersed or suspended in the film former coating solution.

According to this invention, however, electrophotographic coating materials are provided to produce electrophotosensitive coatings on the surface of a sheet or other image carrier base for use in electrostatic or electrophotographic reproduction processes and having water soluble film forming components which can be coated from water solution onto the surface of the sheet or image carrier.

One object of this invention is to produce electrophotosensitive coating materials for use in electrostatic or electrophotographic reproduction processes and including a photoconductive material dispersed in a water soluble film forming and binder component.

A further object of this invention is to produce electrophotographic materials of the character described which may be coated from water solution onto the surface of a sheet or other image carrier base for use in an electrostatic or electrophotographic reproduction process.

Another object of this invention is to produce an electrophotosensitive material which is substantially insoluble in organic solvents.

Still another object of this invention is to produce an electrophotosensitive coating of the character described comprising a water soluble film forming binder which, after having been coated on a sheet or other image carrier base and dried, will exhibit dielectric and electrical properties for use in electrophotographic reproducing processes.

Other objects and advantages of this invention will be apparent from the following description and the appended claims.

It will be understood that, in electrostatic or electrophotographic reproducing techniques of the character to which this invention relates, an electrosensitive film is provided on the surface of a sheet or plate or other image carrier base on which a visible image is to be produced. This film must be capable of retaining an electrostatic charge and includes an electrically insulating film forming and binder component through which is dispersed a photoconductive or photosensitive component adapted to elfect lowering or removal of an electrostatic charge selectively in those areas of the film which are exposed to light.

Considering as illustrative of such an electrophotographic reproduction process the use of a sensitized sheet of paper, an electrophotosensitive film is applied to the surface of the paper. This film, including an insulating or dielectric film forming component and a photoconductive component dispersed therein, is given a uniform negative electrostatic charge in a dark room or otherwise in the absence of light. The charged sheet is then exposed to a light image, as, for example, by projecting an image thereon through a photographic transparency. Wherever the light strikes the charged film on the sheet, the original negative electrostatic charge is lowered or removed through the action of the photoconductive component in the film. This leaves an electrostatic image or charge image on the sheet corresponding to the light image projected thereon.

This charge image or electrostatic image is then developed or made visible by applying to the film a positively charged powder or other finely divided developing agent which will cling electrostatically to those areas of the film which retain the original negative chargei.e., those areas which were not struck by light during exposure to the light image. After the developing agent has rendered the electrostatic image visible, the agent may be fixed to the sheet as, for example, by fusing the developing agent to the sheet and/or spraying the agent with a clear lacquer, etc.

It has been found to be particularly advantageous in the coating or original preparation of the electrophotosensitive sheet or image carrier to apply the electrophotosensitive film or coating thereon from water solution, yet the film forming and binder components of the coating or film must be able to retain the required electrostatic charge at least for the length of time required to expose the film to the desired light image and develop the same.

Satisfactory results have been achieved according to this invention with a number of water soluble film forming and binder materials, and particularly film forming resin polymers having various polar groups or radicals rendering them at least initially water soluble. Also appropriate materials for use according to this invention are capable of being dried after coating and of maintaining themselves more or less continuously dry under normal humidity conditions without the adsorption or absorption of water to an extent which would adversely affect the electrical characteristics of the coating.

Of the various materials appropriate for use according to this invention, the resin polymers having higher molecular weights and a higher proportion of the molecule made up of non-polar groups or radicals are preferred. As illustrative of water soluble film forming and binder components for use in electrophotosensitive compositions embodying this invention are polyacrylic and polymethacrylic acid and ester resins, polyacrylic and polymethacrylic amides, polyvinyl compounds and particularly those with esters, hydroxyl or carboxyl groups thereon rendering them water soluble, yet not forming so much of the molecule as to impair electrical characteristics and/ or resistance thereof. Also appropriate for use according to this invention are copolymer materials which may not be inherently water soluble but which can be made water soluble under certain conditions as, for example, partially esterified copolymers, polyvinyl methyl ether maleic anhydride copolymers partially esterified or part amide, polymethacrylic acid vinyl acetate copolymers, and similar types of resins which may be water soluble when neutralized to an alkaline pH but are not water soluble at an acid pH. These polymers may be characterized as being film forming addition polymers of one or more ethylenically unsaturated monomers, wherein the polymer includes functional groups ionizab le in an aqueous solution containing an electrolyte and wherein said functional groups comprise carboxyl groups. Preferably one or more such monomers is an ethylenically unsaturated carboxylic acid monomer. In addition to the aforementioned water soluble characteristics according to this invention, the film former should have a relatively high dielectric constant and high dielectric strength, and should have sufficient strength and flexibility particularly if the coating is to be applied to paper to withstand bending and handling when coated as a thin film.

As will be understood, of course, such film formers should also be compatible with and substantially inert with respect to whatever photosensitive or photoconductive material is included in the coating. Among the known materials which exhibit electrosensitive or electroconductive properties for use in electrophotographic coatings are such materials as zinc oxide, titanium dioxide, zinc or cadmium sulphide, zinc selenide, and the like, although a commercial grade of zinc oxide (known as Florence Green Seal No. 8, sold by the New Jersey Zinc Co.) and the regular technical grade of titanium dioxide are preferred photoconductor materials.

The selection of a suitable photoconductive component may be made as disclosed in US. Patent 2,898,191 mentioned above. Thus, in order to determine whether or not a particular photoconductive substance is suitable for use in the present invention, a test of its photoconductive properties may be made as follows. A small quantity of the substance is reduced to a powder, the powder is compressed under high pressure, i.e., about 15,000 lbs. per square inch to form a pellet, electrodes, as of silver paste, are applied on a surface of the pellet leaving a square area of surface uncoated, the pellet is placed in a monochromator with the aforementioned uncoated surface area facing the light source, and successive wave lengths of light throughout the spectrum are projected on this surface. A D-C potential is placed across the electrodes and the current flowing between the electrodes is measured as a function of wave length with the intensity of radiation being held constant.

The photoconductive substances which are suitable are those which are substantially electrically non-conductive in the dark. When exposed to light, they should have a surface photoconductivity of a certain level in order to be of practical use in the present process. In testing substances in order to determine their suitability and utilizing a pellet form, it is convenient to express the results of the measurements of the test as a surface photoconductivity because substantially all of the light is absorbed within a thin layer at the surface of the pellet. It has been found that, to be useful in the present invention, the substance selected should have a surface conductivity of at least about l0 /ohm /square/watt/cm. when exposed to some wave length within the range of about 3800-7000 A.

Having established the threshold value of photoconductivity needed in the process, it is possible to test any photoconductive substance otherwise suitable from the standpoint of stability, compatibility, dark resistivity color, etc., in order to determine whether it can be used.

A number of materials are satisfactorily photoconductive for use in electrophotographic processes, but zinc oxide is a preferred photoconductive materials for use according to this invention and can be prepared in a white form or in a pink form. Of the various white zinc oxides commercially available, not all have a surface photoconductivity greater than about l0- /ohm- /square/watt/ cm. at a wave length of about 3900 A. which is about the wave length of peak photosensitivity for this material, but many pure grades of Zinc oxides made by a dry process have been found suitable.

In these compositions, it has been found possible to vary the ratio of photoconductor to the film-forming material over wide limits. The optimum quantity of photoconductor for any given composition will depend upon the particular film-forming ingredient used since these vary considerably in electrical properties such as dielectric constant. It has been found, unexpectedly that relatively pure zinc oxide, such as that designated C.P. or U.S.P. gives much better results in the present process 7 than ordinary technical grade zinc oxide commonly used heretofore in pigments or in coated papers. Although the reason is not understood, zinc oxide having a very low concentration of impurities, when combined with the type of vehicle described herein, is capable of taking and holding an electrostatic charge in the dark and of being discharged in the presence of light.

Herewith are given chemical analyses of impurities found in three typical samples of zinc oxide which were found suitable for use in the process of the present invention.

The physical form of the zinc oxide also has an effect on the optimum amount of this ingredient. There is an appreciable difference in density between zinc oxide powders prepared by wet and dry processes.

White zinc oxide is a preferred photoconductive substance for use in the processes, coated base materials and apparatus of the present invention for a number of reasons. The fact that it is white causes it to be more acceptable for certain uses such as reproducing photographs. It is also relatively abundant and cheap, stable, compatible with synthetic resins and easy to apply as a coating on paper and other bases.

However, it has also been found that a pink form of zinc oxide exhibits desirable photoconductive properties similar to the White zinc oxide but is of the order of several times faster with regard to length of exposure required for incandescent light. Moreover, the pink zinc oxide is responsive to light throughout most of the visible spectrum whereas the white zinc oxide has its peak response in the ultra-violet range.

One method of manufacturing a pink zinc oxide suitable for use in the present invention is described and claimed in US. patent application, Ser. No. 329,473, filed Jan. 2, 1953, Conn et al., assigned to Merck and Company, Inc, now U. S. patent No. 2,898,191. The process described in the said application comprises heating ammoniated zinc carbonate at a temperature of 100-400 C. Preferably, the carbonate is heated at 250 C. for about 1-2 hours or until all of the amounts and carbon dioxide are released. At this point a weight loss of about 43% will be realized and the resulting product will have a particle size of about 100-200 A. The ammoniated zinc carbonate may be first prepared by adding white zinc oxide to a solution of ammonium carbonate in 28% ammonia water, blowing in carbon dioxide until no further separation of solid occurs, filtering out the solid, which is the ammoniated zinc carbonate, washing and drying.

The pink zinc oxide, prepared as above described, may be substituted, weight for weight, for white zinc oxide given in the examples and the compositions suitable for use are also otherwise the same as those shown in the examples.

As noted above, the water soluble binders for use according to this invention may be water soluble only at an alkaline pH. Also some of them (e.g., polyacrylic acid) may form insoluble precipitates with a photoconductor such as zinc oxide at an acid pH, or may change solubility characteristics when partially esterified. For this reason it is necessary with such binders to neutralize the film former solution, preferably before the addition thereto of the photoconductor, so that the resultant composition can be coated from water solution as desired.

The presence, however, of a substantial amount of active alkaline material in the final coating may interfere with the desired electrical properties and/or resistance of the dry coating either because of the presence of electrolytic material and/ or low molecular weight charge carriers or as rendering the coating softenable by absorbed moisture. Thus, in preparing the water soluble coating composition for practicing this invention, it is preferred to use as a neutralizing or solubilizing agent an alkaline material which is volatilizable or which otherwise may be removed from the applied coating during the drying thereof. Satisfactory results have been achieved in this connection using aqueous ammonium hydroxide and/or such volatile organic bases as monoethylamine.

In formulating the electrophotosensitive coating for this invention, it is also important to consider the ratio of photoconductive material to film forming binder. If this ratio is too low, the photosensitivity may be decreased to the point where the electrostatic film will not be adequately discharged even with excessive exposure. Alternatively, if the proportion of the photoconductor is increased, the tendency of the charged film to discharge itself even in the dark and prior to exposure also increases. As will be understood, if too much of the solid photoconductor material is present, the ability of the binder to form a continuous film matrix may be interrupted.

Satisfactory results have been achieved according to this invention with ratios of photoconductor to binder ranging approximately from 2 to 1 up to 25 to 1 by weight, with ratios of at least approximately 3 to 1 and up to 6 to 8 to 1 being preferred. It should also be noted in this connection, that lower ratios may be satisfactory where a high intensity ultra-violet flash is used for the exposure to give deep immediate penetration of the light into the film, whereas higher ratios may give better results with a less intense incandescent light source. The photoconductor thus constitutes a dominant proportion by weight of the solids of the coating material.

As illustrative of coating compositions embodying this invention the following are noted:

Methacrylic acid/vinyl acetate copolymer (sold under the name of Elvalan) grams 75 De-ionized water cc. 415 Aqueous ammonium hydroxide cc. 50 Zinc oxide (sold under the name of Florence Green Seal No. 8) grams 150 Polyacrylic acid solution (containing 36 grams FAA and sold under the name of Goodrite K704) grams 240 De-ionized water cc. 175 Aqueous ammonium hydroxide cc. 50 Zinc oxide grams 144 Methacrylic acid/vinyl acetate copolymer grams 75 De-ionized Water cc. 250 Aqueous ammonium hydroxide cc. 50 Finely divided titanium dioxide grams 150 Polyacrylic acid solution (6.7 grams polyacrylic acid) grams 44.4 De-ionized water cc. 50 Aqueous ammonium hydroxide cc. 18 Finely divided zinc sulfide g-rams 2O Polyacryla'mide grams 15 De-ionized water cc. 300 Zinc oxide grams 75 Aqueous ammonium hydroxide to pH 9.

Polyvinyl methyl ether/maleic anhydride copolymer half amide grams 15 De-ionized water cc. 300 Zinc oxide grams 75 Aqueous ammonium hydroxide to pH 9.

Polyvinyl methyl ether/maleic anhydride copolymer half amide "grams 15 De-ionized water cc. 300 Zinc oxide grams 75 Aqueous ammonium hydroxide to pH 9.

Polyacrylic acid solution (15 grams polymer) grams De-ionized Water cc. 100 Finely divided titanium dioxide grams..

Aqueous ammonium hydroxide to pH 9.5.

In the foregoing examples the photoconductor was dispersed in a water solution of the film forming components, with or without neutralizing or other solubilizing action as noted, and the resulting dispersion is then coated on a paper or metal sheet or other image carrier, and heat treated or dried at around 150 C. for approximately 30 minutes to drive off the water in the coating. The resulting dried film is satisfactorily dielectric and is apparently made up of a matrix of minute discreet particles dispersed and bonded in the polymer resin film. As will be understood the viscosities of the coating materials may be varied over wide ranges as desired and depending upon the manner in which the coating is to be applied to the sheet or other image carrier. The dispersing of the photoconductor in the resin solution and the application of the coating to the base material are accomplished by conventional techniques, and the drying of the applied coating may be by infrared, a drying oven, a vacuum oven, or other conventional techniques which will dry and de-gas the applied coating film. It should also be emphasized, as noted above, that the water in the coating solution should be de-ionized (as by passing through an ionic exchange column) or distilled so as to be substantially free of dissolved electrolytic components which might be deposited with the coating and interrupt or interfere with the desired electrical characteristics of the film forming material.

It will, accordingly, be seen that there is provided with this invention electrophotographic materials which, because of the use of a water solution or dispersion, are less hazardous in handling than other coating materials using organic solvents. Also, water is less expensive as a solvent, and the control of finished film characteristics during application and drying are more readily achieved from a water system. The coating compositions embodying this invention prolong chemical stability and satisfactory physical stability with substantially no settling out of the dispersed photoconductive component.

While the processes and products herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise processes and products and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. In a process of forming an image, the steps of:

providing an electrophotographic image carrier comprising a base material carrying thereon an electrically insulating coating layer including a finely divided photoconductor in a synthetic organic filmforrning addition polymer of an ethylenically unsaturated monomer, said polymer having functional groups ionizable in an aqueous solution containing an electrolyte and wherein said functional groups comprise carboxyl groups,

forming a pattern of electrostatic charges corresponding to said image on a surface of said layer, and developing said pattern of electrostatic charges with an electrostatically attractable material.

2. The process as set forth in claim 1 wherein said polymer is an aqueous soluble polymer of an ethylenically unsaturated carboxylic acid monomer.

3. The process as set forth in claim 1 wherein said polymer is a copolymer of a vinyl ester and methacrylic acid.

4. The process as set forth in claim 1 wherein said polymer is selected from the group consisting of copolymers of vinyl alkyl ethers and maleic anhydride, and the partial esters and partial amides thereof.

5. The process as set forth in claim 1 wherein said finely divided photoconductor is selected from the group consisting of a zinc oxide photoconductor, a titanium dioxide photoconductor, a zinc sulfide photoconductor, a cadmium sulfide photoconductor, a zinc selenide photoconductor, and mixtures thereof.

6. The process as set forth in claim 1 in which said base material is a flexible sheet material.

7. The process as set forth in claim 6 wherein said flexible sheet material is paper.

8. The process as set forth in claim 1 in which said material is metal.

9. In a process of forming an image, the steps of:

providing an electrophotographic image carrier comprising a base material carrying thereon a coating layer including a finely divided photoconductor in an electrically insulating film-forming binder selected from the group consisting of aqueous soluble addition polymers of acrylic acid, methacrylic acid and amides thereof, and addition copolymers of maleic anhydride and partial esters and partial amides thereof,

forming a pattern of electrostatic charges corresponding to said image on a surface of said layer, and developing said pattern of electrostatic charges with an electrostatically attractable material.

10. The process as set forth in claim 9 in which said photoconductor is present in said coating layer in an amount by weight of at least about twice that of said film-forming binder.

11. In a process of forming an image, the steps of:

providing an electrophotographic image carrier comprising a paper base carrying thereon an electrically insulating coating layer including a finely divided zinc oxide photoconductor in a film-forming copolymer of a vinyl ester and methacrylic acid,

said photoconductor being present in said coating layer in an amount between about 2 and about 25 times the weight of said copolymer,

forming a pattern of electrostatic charges corresponding to said image on a surface of said layer, and developing said pattern of electrostatic charges with an electrostatically attractable material.

112. A process of preparing an electrophotographic image carrier comprising a base having thereon an electrically insulating photoconductive coating layer including finely divided solid photoconductor particles in an electrically insulating film-forming polymeric binder covering a substantial portion of at least one side thereof, comprising the steps of:

providing an aqueous solution of an organic film-forming addition polymer of an ethylenically unsaturated monomer, said polymer having functional groups ionizable in an aqueous solution containing an electrolyte and wherein said functional groups comprise carboxyl groups,

said solution containing a sufficient amount of a volatilizable neutralizing reactant to maintain said filmforming polymer soluble therein,

uniformly dispersing in said aqueous solution particles of finely divided photoconductor material in an amount at least twice the amount by weight of said film-forming polymer to form a dispersion wherein the photoconductor material constitutes a dominant proportion by weight of the solids therein, applying said dispersion as a coating over a substantial portion of at least one side of a carrier base to provide a substantially uniform layer thereon, and drying said applied layer with substantial removal of said neutralizing reactant and evaporation of water to form said electrophotographic image carrier.

13. A process of preparing an electrophotographic image carrier comprising a base having thereon an electrically insulating photoconductive coating layer including finely divided solid photoconductor particles in an electrically insulating film-forming polymeric binder covering a substantial portion of at least one side thereof, comprising the steps of:

providing an aqueous solution of an organic film-forming addition polymer of an ethylenically unsaturated carboxylic acid monomer, said polymer having functional groups rendering said polymer soluble in an aqueous solution containing an electrolyte and wherein said functional groups comprise carboxyl groups,

said solution containing a sufficient amount of a volatilizable alkaline neutralizing reactant to control and maintain the pH of said solution such that said filmforming polymer remains soluble therein,

uniformly dispersing in said aqueous solution particles of finely divided photocondulctor material in an amount at least twice the amount by weight of said film-forming polymer to form a dispersion wherein the photoconductor material constitutes a dominant proportion by weight of the solids therein,

applying said dispersion as a coating over a substantial portion of at least one side of a carrier base to provide a substantially uniform layer thereon, and

drying said applied layer with evaporation of water and substantial removal of said neutralizing reactant to alter the pH to form a water insoluble photoconductive electrically insulating layer on said base.

14. A process of preparing an electrophotographic image carrier comprising a base having thereon an electrically insulating photoconductive coating layer including finely divided solid photoconductor particles in an electrically insulating film-forming polymeric binder covering a substantial portion of at least one side thereof, comprising the steps of:

providing an aqueous solution of an electrically insulating film-forming binder selected from the group consisting of aqueous soluble addition polymers of acrylic acid, methaorylic acid and amides thereof and addition copolymers of maleic anhydride and partial esters and partial amides thereof,

said solution containing a sufiicient amount of a volatilizable neutralizing reactant to maintain said filmforming binder soluble therein, uniformly dispersing in said aqueous solution particles of finely divided photoconductor material in an amount at least twice the amount by weight of said film-forming binder to form a dispersion wherein the photoconductor material constitutes a dominant proportion by weight of the solids therein, applying said dispersion as a coating over a substantial portion of at least one side of a carrier base to provide a substantially uniform layer thereon, and

drying said applied layer with substantial removal of said neutralizing reactant and evaporation of water to form said electrophotographic image carrier.

15. A process of preparing an electrophotographic image carrier comprising a paper base having thereon an electrically insulating photoconductive coating layer including finely divided solid photoconductor particles in an electrically insulating film-forming polymeric binder covering a substantial portion of at least one side thereof, comprising the steps of:

providing an aqueous solution of a film-forming copolymer of a vinyl ester and methacrylic acid, said solution containing a sufiicient amount of a volatilizable neutralizing reactant to maintain said film-forming copolymer soluble therein, uniformly dispersing in said aqueous solution particles of finely divided zinc oxide photoconductor in an amount between about 2 and about 25 times the Weight of said copolymer, applying said dispersion as a coating over a substantial portion of at least one side of a paper base to provide a substantially uniform layer thereon, and

drying said applied layer with substantial removal of said neutralizing reactant and evaporation of water to form said electrophotographic image carrier.

16. An electrophotographic image carrier comprising a base member having a layer thereon covering a substantial portion of at least one side thereof and forming a substantially nonhygroscopic photoconductive electrically insulating layer, said layer comprising:

a synthetic organic film-forming addition polymer of an ethylenically unsaturated monomer, said polymer having functional groups ionizable in an aqueous solution containing an electrolyte and wherein said functional groups comprise carboxyl groups; and

particles of finely divided photoconductor material uniformly dispersed in said polymer,

said photoconductor material constituting a dominant proportion by weight of the solids in said layer and being present therein in at least two parts by weight to each part by weight of polymer,

said polymer being present in a sufficient amount to bind said particles to said base, and

said layer having a high electrical resistance in the absence of light.

17. An electrophotographic image carrier comprising a base member having a layer thereon covering a substantial portion of at least one side thereof and forming a substantially nonhygroscopic photoconductive electrically insulating layer, said layer comprising:

a synthetic organic film-forming addition polymer of an ethylenically unsaturated carboxylic acid monomer, wherein said polymer includes carboxylic acid functional groups rendering said polymer soluble in an aqueous solvent containing an electroylte, and

particles of finely divided photoconductor material uniformly dispersed in said film-forming polymer,

said photoconductor being present in an amount from at least 2 to about 25 times the weight of said poly mer and constituting a dominant proportion by weight of the solids in said layer,

said polymer being present in a sufficient amount to bind said particles to said base, and

said layer having a high electrical resistance in the absence of light.

18. An electrophotographic image carrier comprising a base member having a layer thereon covering a substantial portion of at least one side thereof and forming a substantially non-hygroscopic photoconductive electrically insulating layer, said layer comprising:

an electrically insulating film-forming binder selected from the group consisting of aqueous soluble addi' tion polymers of acrylic acid, methacrylic acid and amides thereof, and addition copolymers of maleic anhydride and partial esters and partial amides there of, and

particles of finely divided photoconductor material uniformly dispersed in said film forming binder,

said photoconductor being selected from the group consisting of a zinc oxide photoconductor, a titanium dioxide photoconductor, a zinc sulfide photoconductor, a cadmium sulfide photoconductor, a zinc selc nide photoconductor, and mixtures thereof,

said photoconductor constituting a dominant proportion by weight of the solids in said layer and being present in an amount from at least 2 to about 25 parts by weight to each part by weight of said filmforming binder,

said film-forming binder being present in sufficient amount to bind said particles to said base, and

said layer having a high electrical resistance in the absence of light.

19. An electrophotographic imaging carrier including a base member having a layer thereon covering a substantial portion of at least one side thereof and forming a substantially non-hygroscopic photoconductive electrically insulating layer, said layer comprising:

a film-forming polymeric binder of a copolymer of a vinyl ester and methacrylic acid, and

a zinc oxide photoconductor uniformly dispersed in said film-forming binder,

said photoconductor being present in an amount between about 2 and about 25 parts by weight to each part by weight of binder,

said polymeric binder being present in a sulficient amount to bind said particles to said base, and

said layer having a high electrical resistance in the absence of light.

References Cited UNITED STATES PATENTS Fikentscher et a1. 26029.6 Shipp 260-9l.3 Ball 26029.6 Hayden 117-155 Dalton et al 16 145 X 10 Bacon 91-1 Warthen 96-33 Miles 117-155 Worthen 96-33 Middleton 96-1 Beatty 96-75 X McLaughlin 117-155 Griggs et a1. 96-1 Gundloch 96-1 20 Dalton 96-1 Gundloch 961 Mott 96-1 Clark 96-1 Dalton 96-33 25 Crumley 96-1 2,993,787 7/1961 Sugarman 96-1 3,052,539 9/1962 Grieg 96-1 FOREIGN PATENTS 203,907 11/1956 Australia. 951,469 10/1949 France.

OTHER REFERENCES Sugarman: Electrofax: A New Tool, American Preesman, November 1955, 6 pp.

Sugarman: Electrofax: A New Tool for the Graphic Arts, RCA Publication, November 1955, 6 pages.

Sugarman: The American Pressman, pages 33-38, November 1955.

Elvanal Polyvinyl Alcohol, E. I. du Pont de Nemours, Vinyl Products Division (1953), pages 5-43.

Mees: The theory of the Photographic Process, revised edition, MacMillan C0. (1954), pages 131-137.

NORMAN G. TORCI-IIN, Primary Examiner.

J. C. COOPER III, Assistant Examiner.

US. Cl. X.R. 

